Electronic circuit breaker



Feb. 8, 1949. VO PIGNO 2,460,860

ELECTRONIC C IRCUIT BREAKER Filed OCC. 25, 1945 r b J (\J m m m h L,1

Q l/ S! INVENTOR AMERICO VOLPIGNO AT TORNEY Patented Feb. 8, 1 949UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, asamended April 30, 1928; 370 0. G. 757) 3 Claims.

This invention relates to a protective device for electrical apparatusand is illustrated herein as embodied in a sensitive electronic circuitbreaker adapted to be inserted in the power supply of electricalapparatus.

A conventional circuit breaker of the type which includes a relay devicehaving its coil connected in series with the power supply to electricalapparatus is not sufllciently sensitive for use with valuable andprecise electrical apparatus. Such circuit breakers cannot be made toreact to cut off the power quickly enough to prevent serious damage,when a short occurs in internal circuits.

Therefore, it is an object of this invention to provide a protectivedevice for electrical apparatus which is sufliciently sensitive toremove power therefrom before serious damage occurs.

Accordingly, this invention provides an electronic circuit breakeradapted to be inserted in the power supply of electrical apparatus inwhich a relay in series with an electron tube is used to open the powercircuit when a sufficient poten-- tial is set up between the grid andcathode of the tube, this potential being obtained from a point insidethe electrical apparatus to be pro tected. As a further feature of thisinvention, a second relay and a pair of switches are used to maintainthe circuit open when once broken and to permit manual operation of theprotective device.

With the above and other objects and features in view, the inventionwill now be described with reference to the accompanying drawing whichillustrates a preferred embodiment of the invention and will be pointedout in the claims.

The drawing illustrates schematically an electronic circuit breakerconstructed in accordance with this invention.

In the drawing, terminals connected with a source of power supply areindicated at l2 and [3. The terminal I3 is connected directly byconnection I4 to the electrical apparatus to which power is to besupplied as shown at l5. In series with the terminal 12 are connectedone set of contacts l6 which comprise a portion of 'relay ll.

The relay I! may be a conventional D. C. relay having a coil l8 with acondenser IQ of appropriate capacity across the coil to aid in smoothoperation of the relay. One side of the coil I8 is connected at point tothe connection 23 and thus through relay contacts 24 to terminal l2. Theother side of the coil I8 is connected to the anode of an electron tube25. The cathode of the electron tube 25 is connected to the lead I l.The tube 25 may be an electron tube of appropriate type having a controlgrid 26 and other grids as desired.

The control grid 26 is connected to an arm 21 of a potentiometer 28. Oneside of the potentiometer 28 is connected to lead It and terminal 29while the other side is connected to terminal 30.

For operation of the circuit breaker, terminals 23 and 30 are connectedto some point inside the protected apparatus where the potential changeswhen a short or improper connection is present. For example, theseterminals may be connected across the bleeder resistor of a conventionalrectifier power supply. When a short or improper connection is presentthe voltage across this bleeder resistor decreases and this decreasedpotential applied to grid 26 through potentiometer 28 and terminals 30and 23 would affect the circuit breaker as described herein.

The contacts 24 of the second relay 3| are connected in series with thelead 23 and terminal l2. The coil 32 of the relay 3| is connected inseries between the terminals l2 and I3 with a rectifier tube 33, anormally closed switch 34, and the contacts 35 of relay H. The contacts35 of relay I! are closed when contacts I6 are open and vice versa asindicated by the dotted line joining these contacts. A second switch 36,which is normally open, is connected to bridge the contacts 35.

The filaments 31 and 38 of electron tubes 25 and 33 are connected inseries between terminals l2 and I3 with a resistance 39 of appropriatesize.

The electron tube 33 is, used to provide rectified A. 0. current so thata D. C. relay 3| may be used.

In operation a source of power input is connected across terminals l2and I3. The power input to the apparatus being protected is taken fromterminals l5 and 40.

When the cathodes of electron tubes 33 and 25 are at the normaloperating temperatures and the circuit breaker is operable, the switch34 is opened, removing power from relay 3|. Deenergizing relay 3! causescontacts 24 to close so that power is supplied to point 20. Electrontube 25 will now conduct and the current flowing through relay coil 18and tube 25 energizes relay l1 and closes contacts l6, also openingcontacts 35. Since contacts 24 and I6 are now closed,

' power is supplied from terminal l2 to terminal 40 and thus to theapparatus connected to terminals 15 and 40. Terminals 29 and 30 areconnected to points in the protected apparatus so as to transmit anyvoltage which arises in the apparatus due to shorts or improperconnection therein. When ashort or improper connection is present in theapparatus, the grid 26 of the tube 25 has a smaller signal or potentialapplied to it.

The arm 21 of the potentiometer 28 is adjusted along the resistancethereof to such a point that when shorts or improper connection arepresent in the apparatus, the grid receives a potential such that tube25 will be cut off and no current will flow through it and coil l8. Thuswhen a short or improper connection is present, the tube 25 ceases toconduit, relay I1 is deenergized, contacts I6 are opened, and contacts35 are closed. Opening contacts l6 removes the connection betweenterminals l2 and 40, so that power to the protected apparatus isremoved. In order to maintain this circuit open, contacts 35 of relayII, contacts 24 of relay 3|, and relay 3! are used. At the time contactsI6 ar opened contacts 35 are closed completing a connection fromterminal' I! through switch 34, contacts 35, coil 32, and electron tube33 to terminal l3. Current flowing through coil 32 energizes relay 3|and opens contacts 24. When contacts 24 are open no power reaches pointso that electron tube 25 cannot conduct. Thus relay l1 remainsdeenergized and contacts l6 remain open while contacts are closed. If noshort or improper connection is present in the protected apparatus, grid26 of tube 25 remains at its normal potential and current continues toflow through tube 25, and coil l8 of relay' l1, thus contacts it ofrelay ll remain closed and power is supplied to the protected apparatusat terminals l5 and 40.

Power to the protected apparatus may be removed manually by closing theswitch 36. This switch bridges the contacts 35 of relay H and suppliescurrent to relay 3| to open the contacts 24 and remove power from relayl1 and thus terminals l0 and I5.

While this invention has been described with a particular embodimentthereof it will be understood by those skilled in the art thatmodifications may be made without departing from the invention. It istherefore the aim of the appended claims to cover all such variations asfall within the true spirit and scope of the foregoing disclosure.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for Government purposeswithout the payment of any royalty' thereon or therefor.

Having described the invention, what is claimed as novel and desired tobe protected by Letters Patent of the United States is:

1. An electronic circuit breaker adapted to be inserted in the powersupply of electrical apparatus comprising, a pair of leads for conveyingcurrent from the power source to said apparatus, a relay having itscontacts connected in series with one of said leads and having one endof its coil connected to one of said leads, said relay contacts beingclosed by current through said coil, an electron tube having its plateconnected to the other end of said relay coil and its cathode connectedto the other of said leads, a second pair of leads, one of said secondpair of leads being connected in the grid circuit of said electron tubeand the other of said second pair of leads being connected to one ofsaid first mentioned pair, said second pair of leads being adapted to beconnected to points in said apparatus to transmit any voltage changearising in said apparatus due to shorts or improper connections thereinand bias said grid beyond cutoff and thereby open said relay contacts, asecond relay having its contacts connected in series with said firstmentioned lead and having one end of its coil connected to one side orsecond contacts associated with said first mentioned relay, said secondset of contacts being closed when said first mentioned contacts areopen, the other side of said second contacts being connected to saidfirst mentioned lead, the contacts of said second relay being opened bycurrent through the coil of said second relay, the other end of the coilof said second relay being connected to theother of said leads, wherebthe contacts of said second relay are opened and remain open when saidgrid is biased beyond cutofl.

2. An electronic circuit breaker adapted to be inserted in the powersupply of electrical apparatus comprising, a pair of leads for conveyingcurrent from the power source to said apparatus, a relay having itscontacts connected in series with one of said leads and having one endof its coil connected to one ,of said leads, said relay contacts beinclosed by current through said coil, an electron tube having its plateconnected to the other end of said relay coil and its cathode connectedto the other of said leads, a potentiometer having one end of itsresistance connected to said other lead and having its arm connected tothe grid of said electron tube, the other end of said potentiometerresistance being adapted to be connected to a point in said electricalapparatus to transmit any voltage change arising in said apparatus dueto shorts or improper connections therein and bias said grid beyondcutoff and thereby open said relay contacts, a second relay having itscontacts connected in series with said first mentioned leads and havingone end of its coil connected to one side of second contacts associatedwith said first mentioned relay, said second contacts being closed whensaid first mentioned contacts are open, the other side of said secondcontacts being connected to said first mentioned lead, the contacts ofsaid second relay being opened by current through'the coil of saidsecond relay, a second electron tube having its plate connected to theother side of the coil of said second relay and its cathode connected tothe other of said leads, whereby the contacts of said second relay areopened when said grid of said first mentioned electron tube is biasedbeyond cutoff, and a switch in series with the coil of said second relayadapted to remove current from the coil to permit the contacts of saidsecond relay to close to restore power to said apparatus.

3. An electronic circuit breaker adapted to be inserted in the powersupply of electrical apparatus comprising, a pair of leads for conveyingcurrent from the power source to said apparatus, a relay having itscontacts connected in series with one of said leads and having one endof its coil connected to one of said leads, said relay contacts beingclosed by current through said coil, an electron tube having its plateconnected to the other end of said relay coil and its cathode connectedto the other of said leads, a potentiometer having one end of itsresistance connected to said other lead and having its arm connected tothe grid of said electron tube, the other end of said potentiometerresistance being adapted to be connected to a point in said electricalapparatus to transmit any voltage change arising in said apparatus dueto shorts or improper connections therein and bias said grid beyondcutoii and thereby open said relay contacts, a second relay having itscontacts connected in series with said first mentioned lead and havinone end of its coil connected to one side of second contacts connectedin series therewith and adapted to pro-' vide power in the coil of saidsecond relay and thereby open the contacts of said second relay.

ALCERICO VOLPIGNO.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 472,084 Thum Apr. 5, 18921,741,691 Fenton -1 Dec. 31, 1929 2,001,494 Jones May 14, 1935 2,147,781Ward Feb. 21, 1939 2,165,848 Gothe et al July 11, 1939 2,358,215 DarlingSept. 12, 1944 2,424,298 Bailey July 22, 1947

